An easy way to make some extra money is to sell your unused stuff. However, if you don't know when to sell certain items, you can lose out on some major cash — up to hundreds of dollars, in fact.

Luckily, INSIDER spoke to OfferUp— a popular online and mobile marketplace that rivals Craigslist— to find out what you should sell each month to make the most money possible. Check it out below, and start earning more for your stuff.

All data provided by OfferUp represents average item purchase price.

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First up, January's the best month to sell your TV.

If you bought or received a new TV during the holiday season and want to sell your old one, don't wait too long. OfferUp users who sell their TV within the first month of the year earn an average of $189, compared to just $170 in June.

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Sell engagement rings and other jewelry in February, just in time for Valentine's Day.

If you're itching to sell your old convertible or sports car, wait until March.

According to the DMV, convertibles and sports cars sell best in spring and summer. On OfferUp, people who sell their cars in March see less competition with other listings. They also earn $243 more on average compared to people who sell their cars in February.

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As camping season kicks off in the spring, sell your tents and other camping gear in April.

June's the best month to sell your old baby stroller, as expecting parents prepare for their due dates.

More babies are born in July and August than any other month of the year, according to the most recently available CDC data. You can earn an average of $70 on OfferUp for a baby stroller in June, compared to just $60 in October.